possibility to use charger and battery at the same time

[dorg]

hi everyone :)
i want to make a robot using the frc battery:
http://www.andymark.com/battery-p/am-3062.htm
and this charger:
http://www.andymark.com/Battery-Charger-1-Bank-6-Amp-p/am-2555.htm

the thing is, i want the battery to power the robot, and from time to time connect the charger to the battery in order for it to charge (while it is powering the robot)

is that possible?
if not, are there better solutions? battery charger and such?

thank you,
dor

[Bryce Clegg]

The way the batteries use the cables, they are not meant to be powering the robot and charging at the same time. What most teams do is keep multiple batteries with them, and charging the other batteries while your robot is doing its function.

[MrForbes]

You can do what you want, but you need to consider how much current the robot will use, and how often you will need to charge it, and how long it will take to charge the battery while the robot is running. The current the robot uses while charging, will limit how much current will be able to return to the battery from the charger.

[Alan Anderson]

Unless the charger is specifically designed to work while the battery is being used, connecting it while the robot is powered is very much not a good idea.

[FrankJ]

It is done in cars all the time so it is a theoretical possibility. You need a charger that self limits current so it is not overloaded when the system is drawing more power than the charger can provide.

[Mr V]

It depends on the components used on the robot and the voltage range of the charger. A typical charger will charge at ~14.2 volts while a fully charged battery is only 12.7 volts. Not all chargers are the same however, but most fully automatic chargers will not exceed ~14.4 volts. So if you have any components that can't handle the max voltage the charger can supply they will be damaged. Keep in mind every time you drive your car those components that are normally rated for a nominal 13.8v are subject to that ~14.2v while the car's charger (alternator) is "on" which should be any time the engine is running.

[dorg]

so, if i understand you right when the charger is on and connected all my components in the robot will get the voltage it suplies 14.2 for example?

is there a way to do this without damaging my components with the extra voltage?
are there any recommended chargers for this?

to make myself clear, i am doing an autonomous robot that needs once in a while to charge itself from the AC power dock

[MrForbes]

As Alan suggests, you probably want to use a charger that is designed to do what you want to. The charger you listed above is designed to charge batteries with not other load connected.

I don't know how helpful this is, but I have an old robot called Hero 2000 that has a docking station that it can drive into, and charge. I might have the schematics for it somewhere. It uses a battery similar to the battery you listed, although it has a bit more capacity (24 AH instead of 18 AH).

[dorg]

sure anything will help :)
especially if someone could help me choose a good charger for this application
and can also answer me for the question above:

so, if i understand you right when the charger is on and connected all my components in the robot will get the voltage it suplies 14.2 for example?

is there a way to do this without damaging my components with the extra voltage?
are there any recommended chargers for this?

[rich2202]

is there a way to do this without damaging my components with the extra voltage?


The VRM Module has a rated input voltage of 5 to 16 volts, so it can receive 14 volts. It will output 5 and 12 volts at the rated amperage limits. You can use the VRM to protect electronic circuits.

The Talon motor controller is rated for 6-28 volts, so is fine. I'm guessing that the CIM motors won't have a problem with 14 volts.

[Al Skierkiewicz]

Guys,
Most smart chargers use pulse charging. While the average voltage read by most multimeters will show approx 14 volts, the peak is much higher than that. As I remember, the KOP chargers peaked at something greater than 15 volts. Do not run chargers and robot electronics at the same time. The electronics in cars are designed for all kinds of voltage swings. I remember reading an article that suggested, power supply could be anywhere between 5 volts and 19 volts with a lot of noise on the line. The charge current in an automobile is also generated by a polyphase alternator and the peaks frequency varies with engine speed.

[MrForbes]

How good of a filter is the battery?

[Ether]

Has anyone ever put a scope on the output of a KoP charger and looked at the waveform with a fully charged -- and with a fully discharged -- battery?

[FrankJ]

The battery is pretty good filter. On the more primitive motorcycles, not having a battery in the circuit will fry the electrics. (and more than likely a RoboRio) The better UPSs run on battery all the time with the charging circuits float charging the battery. Not to say that either of these is like the KOP chargers just that this problem has a solution.

[MrForbes]

You read my mind. Although I was just going to do it with a volt meter, since my scope probe got lost on the movie set, and I haven't replaced it. Maybe an analog voltmeter, because it would be so neat to show the students some old technlogy. And I was wondering last night where I put my dad's voltmeter...I found it around 1 AM. Won't see the little transients, but will give us an idea of what the charging voltage is.

[AdamHeard]

You read my mind. Although I was just going to do it with a volt meter, since my scope probe got lost on the movie set, and I haven't replaced it. Maybe an analog voltmeter, because it would be so neat to show the students some old technlogy. And I was wondering last night where I put my dad's voltmeter...I found it around 1 AM. Won't see the little transients, but will give us an idea of what the charging voltage is.

You could film it.

[MrForbes]

Good idea.

[Alan Anderson]

How good of a filter is the battery?

Most batteries are good low-frequency filters, but they don't do much to reduce high-frequency noise or transient spikes -- or the kind of intentional pulses one gets from a "smart" charger.

I'm going to modify my earlier advice. Don't use a battery charger to power a circuit unless 1) the charger is designed for it, and 2) the circuit is designed for it.

[MrForbes]

I did a little poking around with a couple battery chargers. I have a modern charger

http://www.amazon.com/Schumacher-XC6-SpeedCharge-Battery-Charger/dp/B004EIBX00

which I used to charge a battery that had been sitting for a while. It started charging at about 14v and after several seconds the voltage increased gradually to about 16v, then slowly went down to around 14 as the battery charged. I found an old probe and connected my scope, and did not see anything resembling pulsing, transients, etc. The analog voltmeter also didn't show anything to get concerned about.

I also visited the robot room today, and brought my analog volt meter. We have old KOP chargers, which do pulse the battery, as indicated on the "charging" light changing color from green to orange. Video

http://youtu.be/Vf4AfdQVWRo

Maybe it's not as bad as we might think?

[Mr V]

If a battery charger is a quality unit it won't provide pulse voltage unless it has a de-sulfite mode. As noted though some will provide a fairly high equalize charge voltage.

[Al Skierkiewicz]

We have checked battery chargers here at work over many years and several battery technologies. If one just checks the charger connected to a battery, you will find a fairly steady voltage with little transients when the impedance of the connection is low and the battery is almost charged. (Remember that battery internal impedance varies with state of charge) However, the smart chargers are designed to sense battery delta voltage and will regularly switch from charge to sense. If there is any impedance in the line, there will be significant "noise" generated in high impedance paths as they exist. Lead/acid technologies generally perform "constant voltage" charging which by definition is not a low impedance path. The KOP chargers and most of what has been discussed, has #16 or #18 wire which compared to the battery adds significant impedance as well. The addition of a scope probe also grounds the circuit through the scope so that noise that is present may be removed by the method used in examining the noise. Differential scope methods should be used when examining this circuit.